Emergence of a novel PRRSV-1 strain in mainland China: a recombinant strain derived from the two commercial modified live viruses Amervac and DV
Qi Suna1, Hu Xu a1, Chao Lia, Bangjun Gonga, Zhen Lib, Zhi-Jun Tiana, Hongliang Zhanga*
a State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150001, China
b Pingdingshan Center For Animal Disease Control And Prevention, Pingdingshan 467000, China
1 These authors contributed equally to this work.
* Corresponding author contact information: Harbin Veterinary Research Institute, CAAS, No. 678 Haping Road, Xiangfang District, Harbin 150001, China.
Tel.: +86-13624503578
E-mail address: zhanghongliang01@caas.cn
Abstract: Porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) is one of the main pathogens causing porcine reproductive and respiratory syndrome (PRRS). In recent years, the detection number of PRRSV-1 in China has gradually increased, and the PRRSV-1 strains reported in China belong to subtype Ⅰ (Global; Clade A-L). In the present study, a novel PRRSV-1 strain, TZJ2134, was found during epidemiological surveillance of PRRSV-1 in Shandong Province in China. We obtained two fragments of TZJ2134: TZJ2134-L12 (located at nt 1672-nt 2112 in the partial Nsp2 gene) and TZJ2134-(A+B) (located at nt 7463-nt 11272 in the partial Nsp9, complete Nsp10 and partial Nsp11 genes). Phylogenetic and recombination analyses based on the two sequences showed that TZJ2134 is a recombinant strain derived from two commercial PRRSV-1 modified live vaccine (MLV) strains (the Amervac vaccine and DV vaccine strains), forming a new recombinant subgroup of DV+Amervac-like isolates with other strains. However, PRRSV-1 MLV is not currently allowed for use in China. We speculated that TZJ2134 might have been introduced from Europe. This study is the first to provide information on two recombinant PRRSV-1 MLV strains in China and provides new data for the epidemiological study of PRRSV-1 in China.
KEYWORDS: PRRSV-1, Vaccine, Recombination, Novel strains.
1 INTRODUCTION
Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease causing substantial economic losses in the swine industry worldwide. It is mainly characterized by widespread reproductive failure in pregnant sows and respiratory symptoms in pigs of all ages (Butler et al., 2014). PRRSV is divided into two species, namely, Betaarterivirus suid 1 (PRRSV-1) and Betaarterivirus suid 2 (PRRSV-2) (Walker et al., 2020), which share only 50–60% nucleotide sequence identity (Murtaugh, Faaberg, Laber, Elam, & Kapur, 1998) and have attracted increasing attention due to the high incidence of PRRSV mutation and recombination. Based on the phylogenetic analysis of ORF5 nucleotide sequences and the global PRRSV classification system, PRRSV-1 is divided into 4 subtypes: subtype Ⅰ (Global; Clade A-L), subtype Ⅰ (Russian), subtype Ⅱ, and subtype Ⅲ. PRRSV-2 can be divided into 9 subtypes: lineages 1~9 (Shi et al., 2010).
PRRSV-1 and PRRSV-2 have significant differences in geographical distribution. PRRSV-2 was isolated in 1992 in America (ATCC-VR2332, the North American prototypic strain) (Wensvoort et al., 1992) and is mainly prevalent in North America and Asia(Brar, Shi, Murtaugh, & Leung, 2015). PRRSV-1 was isolated in 1991 in the Netherlands (Lelystad virus, the European prototypic strain) (Collins et al., 1992) and is mainly prevalent in Europe. However, only subtype Ⅰ (Global; Clade A-L) has spread to continents other than Europe. The remaining subtypes have been reported only in Eastern European countries and Russia (Stadejek, Stankevicius, Murtaugh, & Oleksiewicz, 2013). In 2011, Chen et al. isolated PRRSV-1 strains (BJEU06-1, NMEU09-1) in China, which was the first report of wild PRRSV-1 isolates in mainland China (Chen et al., 2011). To date, PRRSV-1 has been prevalent in at least 20 provinces in China (Chen et al., 2020; Gao et al., 2017; Liu et al., 2017; X. Wang et al., 2016; Q. Zhang et al., 2020; Zhou et al., 2015). In recent years, the detection number of PRRSV-1 in China has gradually increased. The PRRSV-1 strains reported in China all belong to subtype Ⅰ (Global) and can be divided into four subgroups (NMEU09-1-like, Amervac-like, HKEU16-like, and BJEU06-1-like isolates) (Chen et al., 2017). However, compared with the large number of PRRSV-2 infections in China, the number of PRRSV-1 infections detected was relatively low (Lin et al., 2020; Zhai et al., 2018). We speculated that the reason might be that PRRSV-1 is not given much attention because it is not the main epidemic strain in China, and there is evidence that most PRRSV-1-infected pigs in China exhibit mild clinical symptoms (Ming et al., 2017; X. Wang et al., 2016). Even so, the effect of PRRSV-1 on pigs should not be ignored.
Vaccination is a key strategy for PRRSV-1 prevention and control. In the late 1990s, PRRSV-1 MLV was used in Europe(Chae, 2021). Nevertheless, the particularly high variability of PRRSV and the possibility of vaccine revertant PRRSV emerging in pigs vaccinated with PRRSV MLV could result in recombination between different MLV strains (Eclercy et al., 2019; Kvisgaard et al., 2020) or recombination between MLV strains and wild-type PRRSV strains (Chen et al., 2017; Marton et al., 2019; Wang et al., 2019). This indicates the importance of the rational use of vaccines. In this study, a novel PRRSV-1 strain was identified in the epidemiological investigation of PRRSV in China; this strain was derived from recombination of two commercial PRRSV-1 MLV strains (Amervac vaccine strain and DV vaccine strain).